Question

考虑此表table1

User_ID     Field           Value
1           balance         232
1           last_active     1525690435
2           balance         345
2           last_active     1525690430

要获得用户余额的总和，给定他们的last_active是＆gt; X，我可以使用子查询，如

SELECT SUM(Value) FROM table1 WHERE Field = 'balance' AND User_ID IN (
    SELECT User_ID FROM table1 WHERE Field = 'last_active' AND Value > X
)

有没有更好的方法来获得相同的结果？

Answer 1

不要设计这样的表，当你知道数据结构时使用第3次规范化。
创建索引

Answer 2

您可以编写查询，使其在语法和逻辑上正确（基于您的示例数据）：

SELECT SUM(Value)
FROM table1
WHERE field = 'balance' AND
      User_ID IN (SELECT USER_ID
                  FROM table1
                  WHERE field = 'last_active' AND value > X 
                 );

为了提高效果，我建议EXISTS和table1(USER_ID, field, value)上的索引：

SELECT SUM(t1.Value)
FROM table1 t1
WHERE t1.field = 'balance' AND
      EXISTS (SELECT 1
              FROM table1 tt1
              WHERE tt1.USER_ID = t1.USER_ID AND
                    tt1.field = 'last_active' AND tt1.value > X 
             );

Answer 3

是的，您可以使用exists代替

SELECT SUM(Value) Value
FROM table1 t
WHERE Field = 'balance' AND          
      EXISTS (SELECT 1 
              FROM table1 
              WHERE User_ID = t.User_ID AND
                    Field = ' last_active' AND value > X);

Answer 4

尝试：如果您正在使用单一表格

SELECT SUM(Value) FROM table1 WHERE field = 'balance' AND last_active > X

通过查看查询中的User_ID和ID，您似乎使用了两个单独的表，因此您可以将查询编写为

SELECT SUM(A.Value)
FROM table1 A
INNER JOIN table2 B ON B.id = A.User_Id
    AND B.last_active > 'x'
WHERE A.field = 'field = 'balance'

优化子查询以获得更好的性能？

4 个答案: